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GM Purple Tomato to “keep cancer at bay”

Norfolk’s “healthy” GM tomato was said to have anti-cancer properties – but food safety questions remain

Summary

Extraordinary claims were made for a GM purple tomato’s supposed anti-cancer properties since its development was first announced in 2008. However, these claims have been criticised by health authorities on the grounds that they are not based on evidence. More recently the health claims have been toned down in renewed publicity around the tomato. There are unanswered food safety questions around the tomato, both from the point of view of its high levels of antioxidants – levels that scientists say can harm health – and any unintended changes from the GM process used to develop it. Even at this early stage of the GM purple tomato’s commercialisation, the developer company Norfolk Plant Sciences has used its patents on the GM-obtained enhanced anthocyanin trait to force an avowedly non-GM seed company to stop selling seeds with the same trait, which the seed company said was obtained by conventional breeding.

Facts at-a-glance

A GM purple tomato was genetically engineered with genes from the snapdragon plant to contain high levels of the antioxidant anthocyanin, a type of polyphenol. The GM tomato was developed by Prof Cathie Martin at the John Innes Centre (JIC) in the UK.1

Claims

  • The GM purple tomato was promoted in the media as a supposedly cancer-fighting food. For example, the UK’s Daily Express headlined its 2008 article, “Purple tomato can beat cancer”. The article added that it “could also keep you slim, ward off diabetes and help to safeguard your eyesight”.2
  • The “cancer fighting purple tomato”3 claims were not made up by the press, but originated with the John Innes Centre (JIC), which headed its press release, “Purple tomatoes may keep cancer at bay”.4
  • The claims were based on a small “pilot” study in cancer-prone mice that found the mice eating the GM tomato lived longer than those eating non-GM tomatoes.5

Results

  • The UK’s National Health Service (NHS) and Cancer Research UK (CRUK) objected to the JIC and media claims on the grounds that they are unsupported by evidence. The NHS Knowledge Service said: “Until the tomato is tested in humans we cannot be sure that it will offer the same benefits, or that there will not be any unexpected harms.” 6 Cancer Research UK said it was wrong to assume that “antioxidants = good… that’s not what the science says”.7
  • Evidence indicates that high levels of anthocyanin, such as those in the GM tomato, as well as high levels of polyphenols in general, may present health risks.8
  • In a 2023 press release, Norfolk Plant Sciences toned down previous health claims and did not mention cancer.9 However, it used the word “healthy” to describe the GM tomato and named its US subsidiary Norfolk Healthy Produce.9

Companies

The GM purple tomato is marketed by Norfolk Plant Sciences and its US subsidiary, Norfolk Healthy Produce. Norfolk Plant Sciences is a spinout company from the JIC and the Sainsbury Laboratory and was established by Cathie Martin and her JIC colleague Jonathan Jones.10

Patents

Norfolk Healthy Produce/Norfolk Plant Sciences has used its patents on the GM enhanced anthocyanin trait to prevent an avowedly non-GM seed company selling seeds with the same trait that the seed company said was obtained by conventional breeding.11

Claims

A GM purple tomato was genetically engineered with genes from the snapdragon plant to contain high levels of the antioxidant anthocyanin, a type of polyphenol. The GM tomato was developed by Prof Cathie Martin at the John Innes Centre (JIC) in the UK.1

From the start, the GM tomato was promoted in the media as a supposedly cancer-fighting food. For example, on 27 October 2008, the UK’s Daily Express headlined its story about the GM tomato’s development, “Purple tomato can beat cancer”. The article added that it “could also keep you slim, ward off diabetes and help to safeguard your eyesight”.2

Reuters headlined its article, “Scientists develop cancer fighting purple tomato”.3 Like the Express article, the Reuters piece mentioned a small “pilot” feeding study on cancer-prone mice conducted by Cathie Martin and colleagues, which found that the mice fed the GM tomato lived longer than those fed non-GM red tomatoes.5

The “cancer fighting purple tomato” claims were not made up by the press, but originated with the media work of the John Innes Centre. The JIC had headed its 26 October 2008 press release, “Purple tomatoes may keep cancer at bay”.4

In a 2023 press release Norfolk Plant Sciences toned down the previous health claims for the product and did not mention cancer.9 This suggests that some legal caution had entered the marketing strategy for the tomato.

Yet Norfolk Plant Sciences repeatedly uses the word “healthy” to describe the GMO tomato. Indeed, the company has named its US subsidiary, which announced the favourable outcome of the FDA review of the GM purple tomato, Norfolk Healthy Produce. Norfolk Plant Sciences states that Norfolk Healthy Produce “is actively developing and marketing the next generation of innovative vegetables and fruits”.9

Results

Pushback on claims

The Daily Express and other media following the anti-cancer line were quickly slapped down by the UK’s National Health Service (NHS) and Cancer Research UK (CRUK). According to an article in NHS Choices, reporting the views of the NHS Knowledge Service: “These claims are not actually based on benefits seen in humans, but rather from a small-scale study of mice that were given an extract of genetically modified tomatoes.” The NHS Knowledge Service also noted: “The small sample sizes used mean the results may have occurred by chance. Also until the tomato is tested in humans we cannot be sure that it will offer the same benefits, or that there will not be any unexpected harms.” It concluded that without further research, the claims that these GM tomatoes “can beat cancer” cannot be supported.6

Cancer Research UK wrote on its Science Update blog that “cancer is a complex disease that has lots of ‘causes’… The problem with a lot of the coverage of the super-tomato story is that it misses out on this complexity… There’s also a big – and in our opinion unwarranted – assumption in some of the coverage. And that’s the simple equation that antioxidants = good. There’s a fair amount of evidence that some antioxidants in our foods can help prevent some kinds of cancer in some people. But the complexity of this evidence often gets translated in the media and in advertising to ‘antioxidants prevent disease’. And that’s not what the science says.” 7

Antioxidants: The science

In its pushback against the “anti-cancer” claims for the GM tomato, Cancer Research UK points to a New Scientist article on the health effects of antioxidant supplements. The article cites differing and contradictory findings from various studies and concludes that “at best, antioxidant supplements do little or nothing to benefit our health. At worst, they may even have the opposite effect, promoting the very problems they are supposed to stamp out.” 12

This view is reflected by the findings of a mini-review of the human health effects of a class of antioxidants called polyphenols (which include anthocyanin), as ingested from both food and supplement sources. Authored by scientists from Harvard University and the University of Melbourne, the mini-review emphasises “the need for increased regulation and guidelines for polyphenol consumption and supplementation in order to ensure consumers remain safe and informed about polyphenols”. The scientists point out that supplements taken in pill form may make it easily possible to exceed safe levels, potentially causing serious ailments, such as stroke or increased risk of death.13

Venket Rao, professor emeritus at the University of Toronto’s Dept of Nutritional Sciences, warned of the dangers of overdosing on antioxidants. He said: “We have evidence that antioxidants are good for you, but we also have well-controlled clinical studies showing that at megadoses they could be harmful to you.” 14

The GM purple tomato is a food and not a pill supplement. Nonetheless, the high anthocyanin levels in the tomato may present similar risks as those from supplements, as explained below.

Too much of a good thing?

Former US EPA scientist Dr Ray Seidler said:15 “When consumed in moderation, anti-inflammatory compounds like anthocyanins can have health benefits. But too much of a good thing may not be good. It has been demonstrated that over-consumption of anthocyanins (e.g. when taken as pill supplements) may cause kidney, liver, and thyroid hormone health effects.16 Anthocyanins are part of a group of compounds called polyphenols, which may also limit or interfere with iron absorption.” 17     

Drawing attention to the GM purple tomato’s extremely high anthocyanin levels, Dr Seidler said, “The average American consumes around 12.5 milligrams of anthocyanins per day.18 The anthocyanin content from the GM tomato averages about 500mg per 100g of fresh fruit,19 some 40 times more than the daily average consumption. One hundred grams of tomato is less than half a cup. Other naturally purple and red coloured fruits (sweet cherries, blackberries, strawberries, red raspberries, black grapes) contain anthocyanins in the range of 3-143mg/100g,20 up to 160-fold less than the GM purple tomato.”

Michael Antoniou, a London-based professor of molecular genetics and toxicology, explained the double-edged role of antioxidants, which can benefit or impair health, depending on the individual and the circumstances.

“The health claims around ingesting high levels of antioxidants such as anthocyanins are based on their ability to neutralise reactive oxygen species (ROS). ROS perform vital health-promoting functions.

“However, ROS can also damage molecules (including DNA) and cells, leading to diseases such as cardiovascular disease and cancer. The key to good cell and organ function is maintaining a balance between producing enough ROS to appropriately modulate vital functions but not so much as to bring about damage and disease.

“Ingesting megadoses of antioxidants, such as anthocyanins from even a modest portion of the GM purple tomatoes, could interfere with the delicate balance between too much and too little ROS, leading to negative health outcomes.

Supporting these views, a systematic review of randomised trials on antioxidants by the Cochrane Library found no evidence that they can reduce risk of mortality in healthy or sick people and concluded that some antioxidants can increase the risk of mortality. The authors concluded, “Antioxidant supplements need to be considered medicinal products and should undergo sufficient evaluation before marketing.” 21

This type of in-depth evaluation has not happened with the GM purple tomato, even though it contains higher levels of antioxidants than the levels in the pill supplements that some scientists warn against ingesting.

No evidence of food safety

Prof Antoniou warned that, as the GM tomato has been genetically engineered to change biochemical pathways to produce high amounts of anthocyanin, this could also lead to unintended alterations in the tomato’s composition: “Biochemical pathways are interlinked, so introducing a new core pathway could lead to biochemical changes resulting in the production of novel toxins or allergens.

“And this is the risk from just the intended change. In addition, the GM transformation process (plant tissue culture and plant cell transformation) will inevitably give rise to hundreds or thousands of sites of unintended DNA damage (mutations).22 These wide scale mutations can change patterns of gene function and altered biochemistry and composition, with unknown health consequences.23

“There is no evidence that the developers of the GM purple tomato have carried out the kind of molecular analyses (proteomics and metabolomics) that could help establish whether they only got the change they want, with no unintended changes. As a result, we don’t know if these tomatoes are safe to eat.”

Antibiotic resistance genes

The GM purple tomato contains an antibiotic resistance marker gene (the so-called nptII gene),5 which confers resistance to antibiotics including kanamycin and neomycin. The purpose of these genes in this case is to enable the genetic engineer to check which cells have successfully incorporated the snapdragon genes into their genome.

Controversy has simmered over antibiotic resistance marker genes in GMOs for many years but has never been resolved. The concern is that such genes could transfer to disease-causing bacteria and add to the already serious problem of antibiotic resistance in humans and other animals.

The World Health Organization says, “Although the probability of transfer is low, the use of gene transfer technology that does not involve antibiotic resistance genes is encouraged.” 24

Norway has banned the use of GM varieties containing antibiotic resistance marker genes.25

In the EU, Directive 2001/18 states, “The issue of antibiotic-resistance genes should be taken into particular consideration when conducting the risk assessment of GMOs containing such genes” and recommends that they are phased out from commercialised GMOs by 2008.26 However, the GMO industry failed to do so.

There appears to be no independent assessment of risks posed by the presence of an antibiotic marker gene in the GM purple tomato.

Regulatory status

In 2022 the US Dept of Agriculture (USDA) deregulated the GM purple tomato,27 effectively removing it from the agency’s regulatory framework. In 2023 the US Food and Drug Administration (FDA) sent the developers a “no questions” letter.28 This letter confirms that based on the data supplied by the applicant, the GM tomato “does not raise issues that would require premarket review or approval by FDA”.29

Commercial launch in the US

Following favourable reviews by the US FDA and USDA, the GM tomato was commercially launched in the US in 202430 by Norfolk Plant Sciences and its US subsidiary Norfolk Healthy Produce, under the name “Purple Tomato”.31 Seeds were being sold to home gardeners30 at $20 per pack.32 In 2024 the company got its tomatoes into some supermarkets on the East Coast and was targeting high-end restaurants.33

Conventionally bred purple tomatoes

Heirloom non-GM anthocyanin-rich tomatoes (albeit with lower anthocyanin levels than the GM version34) have long been marketed. Heirloom varieties of purple tomato, such as Black Zebra 35 and Black Krim,36 are available to growers.

In addition to heirloom varieties, the “Indigo” family of conventionally bred purple tomatoes were developed by Jim Myers, a plant breeder and professor at Oregon State University, by crossing genes from wild tomatoes with modern varieties.37

It took Martin and her colleagues at Norfolk Plant Sciences 20 years to successfully genetically engineer the GM tomato.37 In contrast, Myers’s non-GM Indigo Rose purple tomato took just 10 years to develop and was released in 2011.38 There are currently more than 50 cultivars of the Indigos being grown and bred throughout the world. Myers said, “There’s just all this diversity in the Indigo market class that has come about through conventional breeding. With the GMO tomato, it’s taken them all this time and more to get one variety out there.” 37 

Laws on health and nutrient claims

In the EU, nutrition and health claims made for products are tightly regulated and must be “clear, accurate and based on scientific evidence”.39 The EU regulation has been retained in the post-Brexit UK.40

In the US, under the Federal Food, Drug, and Cosmetic Act, health claims on foods or dietary supplements must be authorised by the FDA.41 False or unsubstantiated health claims are in violation of the Federal Food, Drug & Cosmetics Act (FDCA).42 In order for foods to carry an FDA-authorised health claim, “there must be significant scientific agreement (SSA) among qualified experts that the claim is supported by the totality of publicly available scientific evidence for a substance/disease relationship”.43

Claims about nutrient content can only be made for nutrients for which there is a Recommended Daily Intake (RDI) in the Code of Federal Regulations (CFR) Title 2144 – but there is no RDI for anthocyanin in the Code.45

There is no indication that Norfolk Plant Sciences has attempted to validate any health or nutrient claims for the GM tomato, either with the FDA or any other official body.

Companies

The GM purple tomato was developed and is marketed by Norfolk Plant Sciences and its US subsidiary, Norfolk Healthy Produce. Norfolk Plant Sciences is a spinout company from the John Innes Centre and the Sainsbury Laboratory and was established by Cathie Martin and her John Innes Centre colleague Jonathan Jones.46

Patents

Cathie Martin and her Norfolk Plant Sciences colleague Jonathan Jones hold active and pending patents on methods to genetically engineer plants with higher antioxidant compounds, as well as on the plants made with those methods.47

Norfolk Plant Sciences targets seed company over alleged patent infringement

In its 2024 catalogue, Baker Creek Heirloom Seed Company in the US offered a “non-GMO purple tomato”, the Purple Galaxy. It even featured on their catalogue’s cover.

On 19 February 2024, Baker Creek said it was contacted by Norfolk Healthy Produce, which “expressed concern that the Purple Galaxy might have been derived from its patented genetically engineered tomato”.48 Baker Creek immediately withdrew the Purple Galaxy seeds, saying, “Subsequent laboratory testing conducted in conjunction with Norfolk did not conclusively establish a relationship between the Purple Galaxy and Norfolk’s GM purple tomato. Indeed, such contamination should be unlikely in Europe, given its approach to GM crops. But the testing also did not conclusively establish that the Purple Galaxy is truly free of any genetically modified material.” 48

Baker Creek also stated that it “remains steadfast in its commitment to selling only heirloom and open-pollinated, non-Genetically Modified (‘non-GM’) varieties”.49

Baker Creek insists that it did its due diligence: “We sourced the seed for the Purple Galaxy from a plant breeder in Europe – where GM tomatoes are not approved – who has collected rare tomato seeds for decades and grows more than 1,000 varieties of tomatoes annually. We actively followed his attempts to breed a purple flesh tomato over the course of three years. In the beginning, using two varieties, he had a fruit that was definitely not purple; it was a purplish red with a few purple streaks. Cultivating five generations over three years, he ultimately had a beautiful tomato with purple skin and flesh. We then travelled to Europe to see the plants for ourselves.” 49

However, C.S. Prakash, who runs the pro-GMO AgBioWorld website,50 accused Baker Creek of lying and deliberately stealing Norfolk Plant Sciences’ patented germplasm. He posted on X: “Liar, liar… your pants on fire! How Bakers Seeds simply swiped some GMO purple tomato seeds from Norfolk Plant Sciences, gave it a fancy name and marketed it as heirloom tomato to its gullible customers!” 51

Norfolk Healthy Produce unambiguously said the Purple Galaxy was GMO: “Given its remarkable similarity to our purple tomato, we prompted Baker Creek to investigate their claim that Purple Galaxy was non-GMO. We are told that laboratory testing determined that it is, in fact, bioengineered (GMO). This result supports the fact that the only reported way to produce a purple-fleshed tomato rich in anthocyanin antioxidants is with Norfolk’s patented technology. We appreciate that Baker Creek tested their material, and after discovering it was a GMO, removed it from their website.” 52

In the absence of either Baker Creek or Norfolk Healthy Produce posting the lab results publicly, it is impossible to know whether they showed the Purple Galaxy was GMO or not.

All we know is that apparently, the testing company didn’t find the obviously GM transgenes (artificially introduced GM genes) they looked for in their first testing – probably the snapdragon genes – but then Norfolk “suggested additional genes to test for”. According to Baker Creek’s post, these results were inconclusive.48

So did the testing company find the snapdragon genes, which are responsible for the increased anthocyanin levels? Or did it find genes that may be found in the GM purple tomato but which are naturally occurring? If the latter, they are not patent-protected.53 European law, correctly interpreted, does not allow patents on naturally occurring genes.54 

Breeders’ patent fears

Plant breeders are becoming increasingly fearful of inadvertently infringing the patents of seed companies, in particular those of the large multinationals, which have taken to sending threatening letters to the breeders, warning them of the consequences of using their intellectual property.

An article called “Laying claim to nature’s work: Plant patents sow fear among small growers” describes the experience of Adaptive Seeds, an organic seed company. The company was contacted by BASF, the owner of Nunhems, the fourth-largest vegetable breeding company in the world, with a list of varieties of seeds and traits Nunhems had patented. According to the article, “It was an ominous reminder of just how many traits and varieties BASF has control over.”

Adaptive Seeds founder Andrew Still said, “There’s always a general concern that one day they’re going to decide we’re selling something that they think is theirs and they’re going to sue us over that.”

Phil Howard, a professor in the department of community sustainability at Michigan State University, explained that as patent law is complicated and ambiguous, many small-scale breeders don’t know if the seeds they want to work with are patented or not. He said this stifles their freedom to experiment.55

Author: Claire Robinson. Historical original research and review: Jonathan Matthews. Review and editing: Franziska Achterberg. Scientific review: Dr Ray Seidler; Dr Michael Hansen; Prof Michael Antoniou.

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  11. Baker Creek Heirloom Seed Company Facebook post (2024). 19 Feb. https://www.facebook.com/rareseeds/posts/pfbid0k3R5xH5359hqPaP3Vmx6sF8gK3a4Xu4rSCsUw6Cz6J5gE4mqSXoe1bdR29uHsEa2l; Rare Seeds (2024). FAQ: Baker Creek discontinues Purple Galaxy tomato seeds. https://www.rareseeds.com/faq; AgDaily (2024). Seed catalog throws tantrum after listing GMO tomato by accident. 20 Feb 2024. https://www.agdaily.com/news/seed-catalog-throws-tantrum-after-listing-gmo-tomato-by-accident/; Pavia W (2024). Why a British purple tomato is causing a scandal. The Times, 3 May. https://www.thetimes.co.uk/article/the-scandal-of-the-purple-heirloom-tomato-developed-in-a-lab-nwlnnt2nf[↩]
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  15. All quotes from Dr Seidler are from: Robinson C (2024). As GM purple tomato goes on sale to home gardeners in US, dubious cancer claims reappear. GMWatch, 19 Feb. https://www.gmwatch.org/en/106-news/latest-news/20381[↩]
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  17. Mennen LI et al (2005). Risks and safety of polyphenol consumption. Am J Clin Nutr 81(1 Suppl):326S-329S. doi: 10.1093/ajcn/81.1.326S.  https://pubmed.ncbi.nlm.nih.gov/15640498/[↩]
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  19. The Silicon Review (2022). USDA approves the genetically modified purple tomatoes. 13 Sept. https://thesiliconreview.com/2022/09/us-regulators-approve-gm-tomatoes ; Norfolk Plant Sciences (2021). Information supporting a regulatory status review of tomato genetically engineered to produce increased levels of anthocyanins. 31 Jul. https://www.aphis.usda.gov/brs/pdf/rsr/21-166-01rsr-review-submission.pdf[↩]
  20. Healthline (2023). What is anthocyanin? Foods list, benefits, and more. Updated 6 Oct. https://www.healthline.com/nutrition/anthocyanin. Summary is based on data from: Manolescu BN et al (2019). Dietary anthocyanins and stroke: A review of pharmacokinetic and pharmacodynamic studies. Nutrients 11(7):1479. doi: 10.3390/nu11071479. https://pubmed.ncbi.nlm.nih.gov/31261786/[↩]
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  47. Lens.org patent search results, as of 30 Sept 2024: https://www.lens.org/lens/patent/142-512-246-788-300/frontpage?l=en ; https://www.lens.org/lens/patent/172-128-558-724-105/frontpage?l=en ; https://www.lens.org/lens/patent/158-626-006-481-71X/frontpage?l=en ; https://www.lens.org/lens/patent/155-881-460-075-34X/frontpage?l=en ; https://www.lens.org/lens/patent/088-201-907-785-074/frontpage?l=en [↩]
  48. Baker Creek Heirloom Seed Company Facebook post (2024). 19 Feb. https://www.facebook.com/rareseeds/posts/pfbid0k3R5xH5359hqPaP3Vmx6sF8gK3a4Xu4rSCsUw6Cz6J5gE4mqSXoe1bdR29uHsEa2l[↩][↩][↩]
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  53. See, for example, two patents covering the GM purple tomato on Lens.org, which cover genes inserted by transgenesis and/or cisgenesis but not genes from conventional breeding; https://www.lens.org/lens/patent/142-512-246-788-300/frontpage?l=en ; https://www.lens.org/lens/patent/172-128-558-724-105/frontpage?l=en[↩]
  54. No Patents on Seeds! (undated). What is the problem? Accessed 11 Mar 2025. https://www.no-patents-on-seeds.org/en/background/problem[↩]
  55. Scotten M (2024). ‘Laying claim to nature’s work’: plant patents sow fear among small growers. The Guardian, 25 Jan. https://www.theguardian.com/environment/2024/jan/25/plant-patents-large-companies-intellectual-property-small-breeders[↩]
Last updated on September 22, 2025